Superheterodyne receiver control



April 1932 w. VAN B. ROBERTS SUPERHETERODYNE RECEIVER CONTROL Filed Nov. 20, 1929 mun! m1;

INVENTOR WALTER VAN B. ROBERTS ATTORN EY Patented Apr. 12, 1932 UNITED STATES.

PATENT; orifice WALTER VAN 'B. :RClBE-RTS, 0F PRINCETON, NEW- JERSEY, 'ASSIGNOR T0 RADIO 00320- BATION OF AMERICA, A CORPORATION OF DELAWARE SUPERHETERODYNE RECEIVER con'rnor.

Application filed November 20, 1929. Serial No. 408,425.

My present invention relates to heterodyne receiving systems, and more particularly to an improved type of superheterodyne receiver.

In a copending application, Serial Number 351,404, filed on March30, 1929, there was described and claimed a superheterodyne receiver in which there was employed for tuning purposes only a single, variable circuit element whereby the necessity of utilizing a uni-control gang of tuning elements was eliminated. There was further disclosed and claimed in this copending application a superheterodyne receiver free from image frequency interference, (that is to say, free from interference engendered by interfering stations whose frequencies are as much on one side of the heterodyne frequency as the desired signal frequency is on the other side).

These imagejfrequencies were eliminated by subjecting the collected signal energy to a fixed filter circuit, the filtered energy then beingheterodyned with local oscillations of a frequency above the broadcasting range,

there being further employed an intermediate frequency sufficiently high so that all the image frequencies of the desired stations were located entirely above the frequency range of the desired stations, which permitted a low pass filter to separate the desired stations from their images. I

In the case of broadcast stations having frequenciesfrom 550 to 1500 kilocyoles, it is obvious that (the lowest intermediate fre quency, which separates the desired signals from their images is147 5 kilocycles.

, The intermediate frequencies employed in a system described in my aforementioned copending application may be conveniently dividedinto three-ranges. First, the range which includes frequencies from 47 5 to 550 kilocycles; this range is satisfactory exceptv in'three respects:

The oscillator frequencies required in clude part of the'broadcast range, andtherefore'care must be taken to prevent interference between such oscillator and other receiving sets in the neighborhood.

(2) The range of images is not separated by much of an interval from the range of signals, thus making it more difficult to separate the highest signal frequency fromthe lowest image frequency effectively.

The intermediate frequency may be produced as beats between certain pairs of undesired stations. I

Secondly, it may be considered possible to locate the required intermediate frequency within the range of broadcast signal frequencies. This would be a good arrange, ment, if there were any frequencies in the broadcast range free from transmitting stations. Obviously, this'is not practicable in present day broadcasting practice, unless a channel within the broadcastingrange can be ofiicially set aside for emergency situations, it being observed that an intermediate frequency could beemployed within this channel since the occurrence of emergency calls would be very few compared to the useful reception on this channel. A

Finally, the third possible location "of the v intermediate frequency is above the broadcast range. This location has the'advantage that the local oscillator never operates at any broadcast frequency and hence there is less chance of its possessing interfering radiation 'characteristics." Again, the separation ofsignals from image frequencyis easily accomplished in this range; It should be observed that with screen grid tubes a high intermediate frequency can be readily amplified, and by employing low loss circuits in suflicient number a good degree of selectivity can be obtained.

Now, I have found that there still remains one drawback to the utilization of ;a high a certain small numberof transmitting stations having harmonics approximately equal cooperation of the heterodyne oscillations,

and if the effect is sufiiciently pronounced audio signals of certain stations will be heard independently of the local oscillator adjustment. Even if these interfering signals are not heard as audio signals, whistles will be produced as the oscillator tuning dial is tuned past certain positions.

As stated above, the present application is directed towards eliminating the sources of interference specified in the aforegoing paragraph. I have discovered a method of, and devised lneans for, obtaining'beat frequencies in a heterodyne system from the interaction of a local oscillator with desired incoming signals, without at the same time producing beat currents between'two or more incoming signal frequencies, thus eliminating interference caused by applying all frequencies (undesired as well as desired stations) simultaneously upon the frequency changer.

Accordingly, it is one of the main objects of the present invention to provide a highly selective, receiving circuit in which there is employed, for tuning purposes, only a single, variable circuit element, which circuit operates on the superheterodyne reception principle and is free from image frequency interference, and is further provided with means for obtaining beat frequencies from the heterodyning of a local source of oscillations with incoming signal frequencies without simultaneously producing beat currents between incomingfrequency energy and high frequency energy other than energy from said source of local oscillations.

Another important object of the invention is to provide a method forobtaining beat frequencies from the interaction of a local oscillator with an incoming signal frequency withoutv at the same time producing beat currentsbetween two incoming signal frequencies which consists in collecting one ormore signal frequencies, impressing allthe signal frequencies upon a pair of frequency changer tubes, balancing out beat currents caused by interacting signal frequencies, and cumulating the beat currents caused by the interaction of the signal frequencies and the local heterodyne frequency.

The novel features which I believe to be characteristic of my invention are set forth in particularity in the appended claims, the invention itself, however, as to'both its organization and method of operation will best be understood by reference to the following description taken in connection withthe drawing 1 in which I have indicated diagrammatical y a circuit organization whereby my invention may be carried into effect.

Referring now to the drawing which shows diagrammatically a superheterodyne receiver circuit embodying my invention, there is shown a grounded antenna circuit 3, 4. The energy collected in the antenna circuit is impressed upon the input terminals of a low pass filter, the latter comprising a plurality of filter sections made up of inductances 1 and capacities 2, and not passing frequencies above the broadcast range. The filter is equipped with terminating resistances R and R at each end, each resistance being connected in shunt with itsadjacent capacity. The resistance R, is connected in the antenna circuit, as shown.

The output of the filter is connected through a capacity C and a leak R to the midpoint 5 of the inductance 6, the latter being connected in series with the two control electrodes 7, 7 of the space discharge tubes 8, 8'. A variable capacity C, shunted across the inductance 6 determines the tuning of the oscillator circuit. The circuit which includes the tubes 8, 8, the tuned input circuit 6, 6, tickler coils 16, 16 and by-pass condensers 17, 17 is considered the oscillator circuit.

The cathodes of the tubes are connected in series through a resistance 9, which is tapped by a grounded slider member P. The resistance 9 is shunted by a series connection of two by-pass capacities 10, 10, the connection between the capacities being grounded. The midpoint connection to the inductance 6 causes the control electrodes 7 and 7 to be energized in opposite phase.

The anode circuits of the two tubes are connected differentially with respect to a tank circuit I, the latter including an antiresonant connection of a capacity 11 and an inductance 12, the latter being tapped at midpoint 13 by a lead 14 connected to a source of anode current B. The circuit I is fixedly tuned to the intermediate frequenc being employed. The function ofthe tan circuit I is to balance out energies coming from the tubes in like phase, but to cumulate the desired beats which are in opposite phase.

The anode of each tube is connected to a point 15, between the capacity 11 and inductance 12 through a coil 16, regeneratively coupled to the inductance 6. Each anodelead to the circuit I is grounded through a high radio frequency by-pass. capacity 17. The inductance 12 is coupled to an inductance 18, thelatter being disposed in the input circuit of the intermediate frequency amplifier J,

the inductance 18 being shunted by a capacity i 19 for tuning the circuit J to the intermediate frequency employed. It is to be understood that the circuit J may be connected to the usual amplifier, detector and utilization circuits, not shown herein for the sake of sim- 2..

licity..

If the oscillator tubes 8, 8' are not functioning, all currents in the anode circuits due to incoming signals balance out in circuit I, so that no voltage of any frequency can be produced in circuit J coupled thereto. When theoscillator tubes 8, 8 are functioning, however, such components of the anode currents as depend upon the phase of oscillator voltage will accumulate in tank circuit I. Thus, beats will be produced between the incoming signals and the oscillator frequency (which is what is desired), while beats will not be produced between incoming signal frequencies themselves.

The condenser C and grid leak R are provided as a well known means for maintaining bias on the grids, and a resistance K may be inserted between point. 5 and capacity C, if necessary, to prevent parasitic oscillation. The tubes 8 and 8 must be maintainedin proper balance, and slider P is one expedient of adjusting the relative outputs of the two tubes to obtain perfect balance.

While I have indicated and described one arrangement for carrying my invention into effect, it'will be apparent to one skilled in the art that my invention is by no means limited -1nclud1ng broadcast frequencies, means for to the particular organization shown and described, but that many modifications may be employed without departing from the scope of my invention as set forth in the appended claims.

What I claim is 1. A method for obtainingbeat frequencies from the interaction of local oscillations with an incoming signal frequency without at the same time producing beat currents between two incoming signal frequencies which consists in collecting a plurality of signal frequencies, impressing all the signal frequencies upon a pair of frequency changer tubes, balancing out currents in the outputs of the tubes in like phase, and cumulating desired beat currents in the outputs of the tubes which are in opposite phase.

2. A superheterodyne circuit comprising means for collecting signal energy, a filter circuit for suppressing undesired signal frequencies, a frequency changing circuit for producing beat currents in like phase and opposite phase, and a tank circuit for balancing out the currents in like phase and cumulating the beat currents in opposite phase.

3. A superheterodyne circuit comprising means for collecting signal energy, a filter circuit for suppressing undesired signal frequencies outside the broadcast range, a frequency changing circuit for producing beat currents in like phase and opposite phase, and

a tank circuit, resonant to a frequency above the broadcast range, for balancing out the currents in like phase and cumulating the beat currents in opposite phase.

4. A superheterodyne circuit comprising means for collecting signal energy, a filter circuit for suppressing undesired signal frequencies, a frequency changing circuit for producing beat currents in like phase and opposite phase, and a. tank circuit for balancing out-the currents in like phase and cumulating thebeat currentsin opposite phase,

thefrequency changing circuit including a and the tank pair of tubes between th'e'filter frequencies outside the broadcast range, a frequency changing circuit for producing beat currents in like and unlikephase, and

an additional circuit for balancing out currents in like phase.

6. A receiver comprising an aperiodic means for collecting radio frequency energy including broadcast frequencies, means for suppressing frequencies outside the broadcast range, a frequency changing circuit for producing beat currents in like and unlike phase, and an additional circuit for balancing out currents in like phase.

A receiver comprising an aperiodic means for collecting radio frequency energy suppressing frequencies outside the broadcast range, a frequency changingcircuit including a pair of space discharge devices, for producing beat currents in like and unlike phase, and an additional circuit for balancing out currents in like phase.

8. A receiver comprising an aperiodic antenna for collecting radio frequency energy including broadcast frequencies, filter means for. suppressing frequencies outside the broadcast range, a frequency changing circuit for producing beat currents in like and unlike phase, and an additional circuit for balancing out currents in like phase.

9. A receiver comprising means for collecting radio frequency energy including broadcast frequencies, means for suppressing frequencies outsidethe broadcast range, a frequency changing circuit for producing beat frequencies outside the broadcast range, a

frequency changing circuit for producing beat currents in like andunlike phase, and a tank circuit resonant to a frequency outside the broadcast range for balancing out currents in like phase and cumulating currents of unlike phase.

11. A superheterodyne receiver comprising an aperiodic antenna for collecting radio frequency energy including broadcast frequen-- cies, a frequency changing circuit, including a pair of electron discharge tubes having a common input and output circuit, for producing beat currents in like and unlike phase, and a resonant circuit in the common out-- 4- 1,aas,17o

put circuit of 'said tubes, resonant to a frequency above the broadcast range, for balancing out currents in like phase, and cumulating. currents of unlikephase, and a circuit,

5 resonant to a desired beat frequency, coupled to said last mentioned resonant circuit.

WALTER VAN B. ROBERTS. 

